There are several reasons to use a group in a regular expression:

• to change the precedence (e.g. /do(g|or)/ will match 'dog' and 'door')
• to remember parenthesised part of the match in the case of capturing group
• to improve readability

In any case, having an empty group is most probably a mistake. Either it is a leftover after refactoring and should be removed, or the actual parentheses were intended and were not escaped.

Noncompliant Code Example

const dateRegex = /^(?:0[1-9]|[12][0-9]|3[01])[- /.](?:0[1-9]|1[012])[- /.](?:19|20)\d\d(?:)$/; // Noncompliant, useless group at the end
const methodCallRegex = /foo()/;  // Noncompliant, will match only 'foo'

Compliant Solution

const dateRegex = /^(?:0[1-9]|[12][0-9]|3[01])[- /.](?:0[1-9]|1[012])[- /.](?:19|20)\d\d$/;
const methodCallRegex = /foo\(\)/; // OK, matches 'foo()'